1. Technical Field
The present invention relates to the field of thin film write heads.
2. Background Art
Data is stored on magnetic media by writing on the magnetic media using a write head. Magnetic media can be formed in any number of ways, such as tape, floppy diskette, and hard disk. Writing involves storing a data bit by utilizing magnetic flux to set the magnetic moment of a particular area on the magnetic media. The state of the magnetic moment is later read, using a read head, to retrieve the stored information.
Data density is determined by the amount of data stored on an area of magnetic media and depends on how much area must be allocated to each bit. Data on magnetic media is often stored in a line or track. Magnetic media often have multiple tracks. In the case of the disk, the tracks are nested annular rings. More bits per ring and more rings per disk increases data density. Data density, therefore, is determined not only by the bit length, but also by the width of the bit which determines the track width. To decrease bit size, head size is decreased by fabricating thin film read and write heads with smaller track widths. Thin film heads commonly employ separate write and read heads.
Typically write heads do not contact the magnetic media but instead are separated from the magnetic media by a layer of air is or air bearing. Magnetic flux generated between poles of the write head acts across the air bearing to change the magnetic moment of an area on the magnetic media.
Thin film write heads are typically formed by depositing and etching layers of magnetic, non-magnetic, dielectric, and electrically conductive materials to form the structures of the head, such as a core, a conductor winding, and upper and lower pole structures.
The rate or frequency that data is stored to the media is an important measure of the operational performance of the write head. One way to improve the operating frequency of the write head is to reduce the length of the pole structures, such as the yoke, to decrease the head inductance and the magnetic flux rise time. The operating frequency is determined, in part, by the structure of the write head and the materials used. The efficiency of the write head is also increased by reducing the yoke length.
Typical conductor windings of write heads are formed by first depositing a seed layer on a cured photoresist layer. To form the conductor winding, a photoresist pattern is formed on the seed layer by depositing photoresist on the seed layer, exposing to light through a photo mask, and removing a portion to form a trench extending to the seed layer. The trench define the placement and dimensions of the conductor that forms the winding. The conductor winding typically is deposited by electroplating with copper to form the conductor winding within the trench on the exposed seed layer.
After forming the conductor winding, the photoresist pattern is stripped, and a wet chemistry etch is used to remove the remaining copper seed layer. As the seed layer typically is removed by wet chemistry etch, part of the winding conductor material is also etched away. The winding is surrounded with photoresist, which is cured to form an organic dielectric insulation.
Additional conductor windings typically are formed over the above described winding in a similar fashion, and electrically connected to it to form a multi-layered conductor winding.
One problem with the above process is that it limits the minimum dimension of the winding. The distance between corresponding edges of successive conductor turns, referred to as the pitch, and the height of the conductor is limited by photolithographic techniques. As such the height to width ratio or aspect ratio of the conductor is usually less than about 1.5. In addition, the minimum width of the photoresist defining the trench typically is greater than about 0.4 microns.
Another drawback of the above process and structure is that it produces a coil structure with a high overall stack height. Because the pitch is limited and the total length of the coil winding is relatively long, the conductors are often formed having greater height to provide sufficient cross sectional area in order to achieve sufficiently low coil resistance. In addition, a second or even a third winding layer often is formed to increase the number of coil turns without drastically increasing the yoke length to improve the operation of the winding. Also, because cured photoresist is difficult to form in extremely thin layers, the cured photoresist insulation typically formed under the conductor winding significantly increases the overall stack height.
High stack height makes it difficult to control the width of the upper or P2 pole tip in certain write head designs, thus leading to increased track width sigma. The increased stack height can cause problems with focusing and scattering during the exposure process, as well as problems of shadowing during pole trim process.
In addition, high stack height can cause reliability problems, such as cracking of the magnetic yoke material at the apex, or on the sloped surface between the top of the stack and the pole tip. Also, the steep slope associated with the high stack height causes the magnetic properties of the yoke material to degrade.
Furthermore, thermal stability is a problem with the structure described above. There is a large thermal expansion mismatch between the metal and the surrounding cured photoresist. The coefficient of expansion of the cured photoresist xcex1resist is greater than or equal to about 10 times the coefficient of expansion of the conductor xcex1metal. This can cause separation of yoke from the underlying insulation when the head is heated to higher temperature during manufacture, or operatation.
The present invention provides an improved thin film write head and method of fabrication. The structure and method of the fabrication allow for an ultra-short yoke and/or an ultra-low stack height.
The present invention reduces yoke length and stack height by forming the conductor winding in trench etched from an insulation layer. With the preferred embodiment, the insulation layer is formed of an inorganic material which is etched using a resist mask to define the width of the trench. Preferably, the insulation layer is formed on planarize layer formed of a different inorganic insulation material. The inorganic materials should be selected so that the etching process may be stopped, or slowed, at the underlying planarized layer.
In the preferred embodiment, the conductor winding is formed on the underlying planarized layer by depositing conductor material so that it fills the trench. Conductor material deposited outside the trench is removed by planarization, such as by chemical mechanical polish, to form the conductor winding. An insulation layer, either organic such as cured photoresist, or inorganic such as Al2O3 or SiO2, may be deposited on the planarized surface of the conductor winding to insulate it from an overlying yoke. The overlying insulation layer may also define the apex angle of the head.
The present invention may have multiple layers of conductor winding. The subsequent layers of conductor may be formed similar to the first layer, or may be formed with conventional photoresist processes and structures.
The present invention is capable of being formed with any known pole structure. For example, embodiments of the present invention may employ pedestal pole tips that are integrally formed, or separately, formed from the yoke, or pole structures. Furthermore, the conductor winding may be formed on a middle coat, a write gap layer, a sub-write gap layer, or other suitable layer.
The present invention allows coil pitch to be reduced. The aspect ratio of the trench and of the insulation between the turns is not limited as in the conventional photolithographic process. With the present invention, the photoresist mask is used to define the width of the trench and distance between the turns of the trench, while the etch process defines the depth of the trench. As such, the turns of the conductor winding may be formed closer together and with higher aspect ratio.
For example, the preferred embodiment and method of fabrication allows a coil pitchxe2x89xa62 microns, and even as small as 0.4 microns. In addition, the conductor width may be as small as 0.18 microns, and turn spacing as small as about 0.1 microns. Furthermore, coil height/width ratio may be as high as 8:1.
The improved aspect ratio allows more turns in a single layer of winding. As such, in some applications a second layer of conductor winding may be unnecessary, thus reducing the stack height. Reducing the stack height also reduces the length of the yoke and thus reduces the flux path length through the yoke.
Also, the present invention allows the coil pitch to be reduced by reducing the spacing between winding turns, or by producing a higher aspect ratio conductor. Thus, the yoke length from the air bearing surface may be reduced.
With the preferred embodiment, stack height may also be reduced by eliminating the organic insulation layer typically found below the conductor winding. In addition, as inorganic insulation layers may be deposited thinner than organic insulation, the preferred embodiment and method of fabrication allows for reduced stack height.
Yet another advantage of the structure and method of the present invention, is that it allows for a reduced number of curing cycles. Typically, multiple resist layers are cured to form organic insulation. With the preferred embodiment, only one curing bake is used to effect insulation of the conductor winding. Limited exposure to curing heat improves yields and reliability.
A further advantage of the structure of the preferred embodiment is that the conductor winding is formed adjacent to inorganic material. The inorganic material provides improved heat dissipation over organic insulation so limits temperatures, thus improving the reliability of the head.